1. Field of the Invention
The present invention is relates to a method for manufacturing a light-emitting panel and more particularly to a web fabrication process for manufacturing a light-emitting panel.
2. Description of Related Art
A number of different methods have been used or proposed for construction of plasma panel display devices in which a plasma-forming gas is enclosed between sets of electrodes which are used to excite the plasma. In one type of plasma display panel, wire electrodes are placed on the surfaces of parallel plates of glass so that they are spaced uniformly apart. The plates are then sealed together at the outer edges with the plasma forming gas filling the cavity formed between the parallel plates. Although widely used, this type of open display structure suffers from numerous disadvantages. The sealing of the outer edges of the parallel plates and the introduction of the plasma forming gas are both expensive and time-consuming processes, resulting in a costly end product. In addition, it is particularly difficult to achieve a good seal at the sites where the electrodes are fed through the ends of the parallel plates, which can result in gas leakage and a shortened product life. Another disadvantage is that individual pixels are not segregated within the parallel plates. As a result, gas ionization activity in a selected pixel during a write operation may spill over to adjacent pixels, thereby raising the undesirable prospect of possibly igniting adjacent pixels. Even if adjacent pixels are not ignited, the ionization activity can change the turn-on and turn-off characteristics of the nearby pixels.
In another type of known plasma display, individual pixels are mechanically isolated either by forming trenches in one of the parallel plates or by adding a perforated insulating layer sandwiched between the parallel plates. These mechanically isolated pixels, however, are not completely enclosed or isolated from one another because there is a need for the free passage of the plasma forming gas between the pixels to assure uniform gas pressure throughout the panel. While this type of display structure decreases spill over, spill over is still possible because the pixels are not in total electrical isolation from one another. In addition, in this type of display panel it is difficult to properly align the electrodes and the gas chambers, which may cause pixels to misfire. As with the open display structure, it is also difficult to get a good seal at the plate edges. Furthermore, it is expensive and time consuming to introduce the plasma producing gas and seal the outer edges of the parallel plates.
In yet another type of known plasma display, individual pixels are also mechanically isolated between parallel plates. In this type of display, the plasma forming gas is contained in transparent spheres formed of a closed transparent shell. Various methods have been used to contain the gas filled spheres between the parallel plates. In one method, spheres of varying sizes are tightly bunched and randomly distributed throughout a single layer, and sandwiched between the parallel plates. In a second method, spheres are embedded in a sheet of transparent dielectric material and that material is then sandwiched between the parallel plates. In a third method, a perforated sheet of electrically nonconductive material is sandwiched between the parallel plates with the gas filled spheres distributed in the perforations.
While each of the types of displays discussed above are based on different design concepts, the manufacturing approach used in their fabrication is generally the same: a batch fabrication process. It would be desirable to simplify and streamline the manufacturing process and to eliminate at least a portion of the steps which can have a negative impact on process yield and/or cost. The present invention is directed to such a method.
According to the present invention, a novel flexible plasma display panel and methods for making such a panel involve a web fabrication process. In this display panel, the plasma forming gas is sealed in transparent micro-components formed of a closed transparent shell. The micro-components, which may be spheres, capillaries or virtually any other three-dimensional shape, are then coated with phosphors to emit one of the primary colors: red, green or blue. In the web fabrication process, a nonconductive flexible first substrate has electrodes imprinted thereon using known printing techniques, such as lithography or screen printing. In one variation, dimples are embossed in the first substrate to define locations at which micro-components are to be placed relative to the electrodes. In another variation, the micro-components are electrostatically drawn to the correct locations relative to the electrodes. After affixing the micro-components in place, and possibly testing to ensure complete and proper placement of the micro-components, a second substrate, also in web form, is disposed over the first substrate so that the micro-components are sandwiched between the first and second substrates. Additional electrodes may be patterned on the second substrate, and the second substrate may be applied as more than one layer to create one or more dielectric/electrode sandwiches near the micro-component to provide additional sustain electrodes or addressing electrodes. Alternatively, the second substrate can be preformed with embedded electrodes which are then aligned with the micro-components when the second substrate is applied. A protective layer may be placed on top of the second substrate, then the layered assembly is diced to form individual light-emitting panels of the desired size.
In a second embodiment of the present invention, a light-emitting panel is formed on a first substrate comprising a flexible web material. A conductive film is patterned on the first substrate to define a plurality of electrodes and dimples are formed to define locations in which gas-filled micro-components, which emit light when excited, are to be located. An adhesive material may be deposited into the dimples. The micro-components are then applied to fill the dimples, where they are held in place by the adhesive. Application of the micro-components to the first substrate can be achieved by a number of different methods including use of a drop tower or an ink-jet type dispenser, or by running the first substrate through a shaker bath filled with an excess of micro-components. An electrostatic charge may be applied to the first substrate to draw the micro-components to the desired locations. After the micro-components are affixed to the first substrate, a liquid dielectric material is applied to the surface of the first substrate using known methods such a vacuum or atmospheric coating, which may include chemical vapor deposition (CVD), plasma sputtering, electron-beam deposition, injection of coating fluid under pressure, screen printing or similar processes. The conditions under which the liquid dielectric are applied, e.g., the surface energy and surface tension of the liquid, are selected to ensure good wetting of the micro-components, i.e., so that the dielectric material is in contact with the surfaces of the micro-components without bubbles or gaps. Further, the liquid dielectric should be applied with a uniform thickness across the first substrate so that the spacing between the excitation electrodes is uniform across the display. Depending on the deposition process that was used, the liquid dielectric is then cured to remove any solvents and other volatile agents that were included in the liquid to facilitate fluid delivery, leaving the micro-components embedded in the flexible, cured dielectric layer. In a preferred embodiment, the liquid dielectric is coated so as to form a dielectric layer with a thickness corresponding to about half the height of the micro-component, allowing a mid-plane conductor to be formed near the micro-components.
Electrodes are formed by applying a conductive liquid to the upper surface of the dielectric layer. The electrodes may be patterned using known lithographic methods, e.g., conductive film deposition, photoresist deposition, masked exposure and development of the photoresist followed by etching to remove the unprotected film, or by printing, e.g., ink-jet printing with a conductive ink. In an alternative embodiment, conductive liquids that are selectively drawn to the desired locations using one or more characteristics of the liquid including surface tension, viscosity, thickness and electrical conductivity in combination with surface characteristics of the dielectric layer. For example, where channels or depressions in the dielectric layer may act as guides for distribution of a liquid conductor to the desired locations near the micro-components, so that no alignment is required in the step for forming the electrodes.
A second application of liquid dielectric material coats the upper surface of the previous dielectric layer, mid-plane conductor and the surfaces of the micro-components above the mid-plane point. An additional sequence of depositing a liquid dielectric and a patterned conductive film may be added before xe2x80x9ctopping offxe2x80x9d the layers with a final coating of liquid dielectric to form a layer that approaches, but not does not cover, the tops of the micro-components. A protective cover layer is then placed over top of the entire assembly, then the panels are diced into the desired dimensions. The cover layer is preferably a web material that may be applied according to known web manufacturing methods.
In an alternate method for patterning of electrodes using photolithographic methods, after formation of a conductive layer, a coating of photosensitive material, e.g., photoresist, is disposed on top of the conductive layer. A contact mask is formed using a flexible optical waveguide having a surface area which covers all or a significant portion of the light-emitting panel. During formation of the waveguide, the cladding material is patterned to allow light to escape from the waveguide at selective locations corresponding to locations of the electrodes to be defined. The photoresist is exposed at the desired locations by light xe2x80x9cleakingxe2x80x9d from the waveguide, then the waveguide mask is removed. After the photoresist is cured and the unexposed resist is removed, the conductive material is selectively etched to form the electrodes at the desired locations.
Other features, advantages, and embodiments of the invention are set forth in part in the description that follows, and in part, will be obvious from this description, or may be learned from the practice of the invention.